Production of titanium dioxide



Patented July 10, 1951 PRODUCTION OF TITANIUM DIOXIDE Ignace JosephKrchma, Wilmington, and Holger Heinrich Schaumann, Newark, Del.,assignors to E. I. du Pont de Nemours & Company, Wilmington, DeL, acorporation of Delaware No Drawing. Application July 25, 1947, SerialNo. 763,738

9 Claims. (01. 23202) This invention relates to the production ofimproved titanium dioxide pigments, and more particularly to novelmethods for producing such pigments through the vapor phase oxidation ofcertain metal halide mixtures under controlled conditions of reaction.

In the co-pending application of Holger H. Schaumann, Serial No.653,428, filed March 9, 1946, (issued as U. S. Patent 2,488,439, datedNovember 15, 1949), highly-useful methods are disclosed for obtainingpigment-quality titanium dioxide through the vapor phase oxidation oftitanium tetrachloride. In accordance with that application, an anataseor rutile pigment is produced by conducting the gas phase decompositionof titanium tetrachloride in the presence of small, regulated quantities(preferably from 0.1% to 5% by volume) of added water vapor tocontinuously form and effect the reaction in the presence of a T102nucleating agent adapted to promote and insure production of ahigh-quality, uniform type of TiOz pigment.

Although its essential pigment properties are satisfactory, the T102product from said Schaumann oxidation process is acidic in character,having a pH of 4-5. This acidity which is very undesirable is due to itsfree halogen (chlorine) or halide content and renders the productnonadaptable for immediate pigment use. This halogen content cannot becompletely removed except upon resort to an expensive, time-consumingwet treatment with an alkaline neutralizing solution, such as ammoniumhydroxide, sodium carbonate, sodium hydroxide, etc., and after suchneutralization the pigment must be dried, calcined and mechanicallyground or pulverized to eliminate aggregates present and insure recoveryof a product exhibiting satisfactory fineness. Certain disadvantagesarise from this neutralizing :after-treatment, including the tendency ofthe pigment to objectionably discolor or yellow when employed in hightemperature or baked refrigerator types of paints and enamels, and thefailure of the required grinding treatment to reproduce the fineparticle size characterizing the original precipitate. Hence, the finalpigment has lacked discoloration resistance in high temperature coatingcompositions and is necessarily coarser in texture than desired.

It has now been found that if the titanium tetrachloride oxidationprocess contemplated in the disclosure of said Schaumann application iseffected in the presence of a relatively small amount of aluminumchloride which also forms a white, water-insoluble oxide during theoxidation, the above neutralizing treatment need not be resorted to, andthat residual halogen present in the recovered TiOz precipitate can beeffectively eliminated upon direct calcination in the temperature. Ithas also been found that the product from such mild calcination willadvantageously comprise a substantially neutral (pH 6.5-'7.5) T102product and will be softer in texture and more readily ground tosuperfineness to yield a particle size commensurate with that of theoriginal T102 precipitate. In addition, the pigment will be improved inhiding power, tinting strength, color, and other essential pigmentqualities. When employed in coating compositions, it will improve thefilm color of such compositions; will decrease the baking discolorationheretofore encountered in oleoresinous and synthetic resin vehicles;will improve resistance to yellowing on exposure in architectural andrefrigerator enamels; and will desirably increase pigment chalking andfading resistance upon employment in exterior coating compositions orfinishes, such as paints and automotive enamels.

These and other advantageous results and benefits are attained in thisinvention which comprises obtaining an improved type of pigmentqualitytitanium dioxide, in either the rutile or anatase crystalline form bydecomposing in the vapor phase titanium tetrachloride and a small amountof aluminum chloride under controlled oxidation conditions and in thepresence of small, regulated quantities of water vapor.

More specifically and-preferably, the invention comprises producingpigment-quality rutile by reacting in the vapor phase, at elevatedtemperatures and over a controlled time period, a mixture of relativelypure titanium tetrachloride and an amount of aluminum chlorideequivalent to from .3% to 3% A1203, based on the amount of titaniumpigment being produced, with an oxygen-containing gas in the presence offrom 0.1% to 5% by volume (based on the total volume of gases present)of water vapor, and thereafter subjecting the recovered pigment to a,mild calcination followed by milling treatment.

In practically adapting the invention, vaporized, anhydrous titaniumtetrachloride'containing a small amount (equivalent to from .1% to 10%as the oxide) of vaporized aluminum chloride, capable of yielding white,insoluble aluminum oxide, is continuously and separately introduced intoa suitable reaction vessel or zone maintained at a substantiallyconstant temperature ranging, say, from 900-1200 C., and wherein themixture becomes thoroughly commingled and substantially completelyreacted with an oxygen-containing gas, such as air, which has beenenriched with from, say, 0.1% to 5%, of water vapor. As a result of suchcommingling, substantially complete oxidation of the halide mixturetakes place with formation and production of a 'IiOz product containingas an essential ingredient a small amount (from, say, .l% to 10%, basedon the T102) of dry state and at a relatively mild, say 600 0., 00aluminum oxide from the diluting or modifying volatile halide reactedalong with the T1614. Prior to such introduction, each reactant may, ifdesired, be preheated to a temperature sufficient to.

insure its reaction when brought together in the reaction zone with theother reactants and within the temperature range mentioned. In efiectingsuch mixing and reaction, any conventional, corrosion-resistant type ofmixing and reaction vessel can be employed herein, provided it is. of adesign, construction and dimension that a continuous flow of reactantsand products of reaction within and through the oxidation chamber willbe afforded and such control can be exercised over the velocities,mixing rates, temperatures, and reactant retention times employed that,on the average, said reactants will remain in said zone for but alimited, short period of time; that ,is, long enough to enable asubstantially complete reaction to take place but less than the timewhich would result in the occurrence of undesired pigment particle sizegrowth. Employing the range of temperature indicated, reactant retentiontimes ranging from .1-1 second are preferred for use since completeconversion of the mixed halides to their corresponding oxides occursWithin such time. Preferably also, and to obtain optimum resultshereunder, use of the highly efficient slot-jet type of apparatusdisclosed in the copending application of Oswin Burr Willcox,

.Ser. No. 763,286, filed July .24, 1947, is resorted to I herein. Thisapparatus comprises an elongated mixing and reaction vessel ofrelatively restricted cross-section into which the involved reactantsare separately fed at controlled velocities and their admixture andreaction is eifected therein,

1 jected to substantially immediate cooling in order to reduce itstemperature to below 600 C. and Weight per hour, to the upper portion ofa Vera! preve t undesired growth of TiO2 pigment particles which wouldotherwise objectionably occur by reason of the cementation or sinteringof loosely-bound pigment aggregates present. The desired quenching canbe effected by resorting to any conventional type of effective coolingopera- 7 tion, such as by recirculating cooled product 7, circulated,cooled product gases or cold solids material thus employed should, asalready noted, be sufficient to drop the temperature of the hotsuspension to below about 600 C. and within less than and not to exceed10 seconds time. The TlOz pigment product can be recovered from thecooled reaction products by conventional separatory treatments,including cyclonic or electrostatic separating media, filtration throughporous media, or the like.

Following recovery, the modified, composite dry state, to a relativelymild calcination treatment until desired chlorine removal becomeseffected. By mild is meant a calcination temperature below that at whichthe primary TiOz particles grow by sintering. Such temperature shouldnot exceed 800 C. and usually ranges from 500-700 C., with a temperatureof about 600 C. being preferred for use. Thereafter, the chlorinefreedproduct is subjected to milling, grinding or disintegration treatment toremove aggregates and can be finished in conventional milling means,such as a hammer or roller type mill or a disintegrator to obtain thedesired small-pal ticle-size pigment. In its finished state, the pigmentwill be uniformly small in size, its average particle size radiusranging from .05 to .5 micron, and preferably from .1 to .25 micron.Being substantially neutral (pH 6.5-7.5), uniformly small in particlesize, soft-textured, and of inherently high tinting strength, color,opacity and other essential pigment properties, it will be generally andreadily adapted for use in all types of pigment applications, such aspaints, enamels, finishes, or other types of coating compositions, aswell as a delusterant for rayon, nylon, or other artificial fibers orsilks or as an essential pigmenting ingredient in printing inks, rubber,plastics, and other uses. Because of its high resistance towarddiscoloration and yellowing, it is outstandingly and particularly usefulin high temperature or baked refrigerator types of paints and enamels.

To a clearer understanding of the invention, the following examples aregiven. These are merely illustrative and not intended to be inlimitation of the underlying scope and principles of the invention:

Example I A vaporized mixture consisting of 98% by volume of titaniumtetrachloride and 2% by Volume of aluminum chloride, preheated to 920 C.in a corrosion-resistant preheater, was continuously admitted, at a rateequivalent to 140 parts 19.?

cal, corrosion-resistant reaction chamber maintained at a temperature of1170 C. Simultaneously therewith, humidified air, similarly preheated toabout 900 C. and containing sufficient added water vapor to provide a.95% E content by volume, was continuously admitted to said chamber, ata rate equivalent to 26 parts by weight of 02 per hour, through aseparate inlet adjacent said mixed metal chloride inlet. The separateinlets through which said reactants were so admitted were so arrangedwith respect to each other that the gas streams entering the chamberconverged immediately upon their introduction and the reactants becamerapidly and substantially instantaneousl mixed together in the upperpart thereof. The flow rates used provided an average retention time ofreactant gases and products within the reaction zone of about .5 of asecond. The gaseous suspension of composite T102 which resultantlyformed within such zone issued from the bottom thereof at a temperatureof approximately 1130 C. and upon its emergence therefrom was subjectedto quick quenching to drop its temperature to 300 C. in less than 2seconds by introducing sufiicient cold chlorine gas therein. Thecomposite titanium dioxide pigment product was then separated andrecovered from the reaction products in filter containers, followingwhich it was subjected to type T102 pigment product is subjected, i thecalcination, in the dry state, at a temperature of 600 C. for a periodof 90 minutes. It was then dry ground in a, hammer mill to effectaggregate removal.

The above process was operated continuously with substantially 100%conversion of the titanium tetrachloride and aluminum chloride takingplace. The pigment product had a pH value of 7.0 and its titaniumdioxide component on X-ray analysis was found to consist entirely ofrutile. It was of excellent soft texture, was uniformly small inparticle size (had an average particle size radius of .165 micron) andits tinting strength and color values were, respectively, 192 and 20:2Y.Its baking discoloration value was very high, being at a value of 20,and its resistance to yellowing in a typical refrigerator enamel wasexcellent.

For comparative purposes, this example was duplicated in all respects,except that in one instance (pigment A below) aluminum chloride was notpresent as a reactant; while in another instance (pigment B below),water vapor was not present during the oxidation. From these tests thefollowing results were obtained:

the reacting zone.

mixture consisting of 97.7% by volume of 'IiCl 'k and 2.3% by volume ofAlCls. This vaporous mixture was continuously fed to a slot jet type ofmixing and reaction vessel, constructed of silica, and of a typedisclosed in the co-pending application of Oswin Burr Willcox, Ser. No.763,286, filed July 24, 1947. This device comprised a central, verticaltubular element having a 2" internal diameter in which, intermediate itslength, was provided a continuous, transverse peripheral slot opening inwidth. The area below said slot was 20 in length, comprised the reactionzone portion of said device. The TiCl4-A1Cl3 vaporous mixture wascontinuously fed through said slot opening in the form of a sheetedstream at a rate of 30.4 mols per hour, while simultaneously air,preheated to 930 C. and to which 0.5%by volume of H20 had previouslybeen added, was separately and continuously fed into the device througha separate inlet of the tubular element remote from the slot inlet toflow downwardly therethrough past said peripheral slot and. into Thevaporous chloride mixture, flowing as a thin, sheeted stream from the(The pigment values given above and throughout this specification weredetermined in accordance with the methods outlined or referred to in U.S. Patents 2,253,551 and 2,046,054. The baking discoloration valuesgiven were determined by incorporating a pigment prepared in accordancewith this invention in an automotive type of finish formulated largelywith modified alkyd resins of the oxidizing type or combinations thereofwith oil-modified phenol aldehyde resins, vinyl resins, etc., and thenapplying the resulting formulation as a coating to a panel and bakingthe coated panel at 180 C. for 1%. hours. Any changes in color due tothe action of heat are compared with those of a similar coatingcompounded with a standard pigment of high quality which has beensimilarly applied to a panel and baked. This control panel isarbitrarily given a number rating of 18. The test paint or coating ispenalized 1 point for the least visually detectable discoloration ascompared with the control. Conversely, if the control paint is observedto have discolored more than the one under test, the latter is given arating correspondingly higher than 18. The best grades of paint pigmentsgenerally have a BB rating of 14 to 20. The yellowing resistanceproperties of a pigment can be readily ascertained through visualinspection and comparison of a paint or enamelcoated panel containingsuch pigment and another panel coated with the same formulation butcontaining a high-grade commercial TiOz pigment. exposure of the panelsfor a definite period of time to direct weathering or simulatedatmospheric conditions in an exterior type of coating composition orafter exposure in an interior type of finish subjected to diffused orindirect lighting.)

Example II Aluminum chloride vapor at a temperature of 860. C. was addedto a stream of vaporized titanium tetrachloride at 920 C. to form avaporized Such comparison is made after the outer periphery of the.tubular element and in a direction radial to the direction of flow ofthe oxidizing gas, became quickly mixed and reacted with the latter at apoint substantially immediately adjacent and below the peripheral slotinlet. The reaction zone was maintained at a temperature of 1050 C. andthe reactants remained within said zone for a period of only .21 second.The resulting gaseous suspension of composite TiOz pigment wasdischarged at a temperature of approximately 1030 C. from the reactionzone and lower extremity of the tubular element, and was quicklyquenched to drop its temperature to 250 C. in less than 2 seconds byintroducing therein sufficient cold chlorine gas. The composite pigmentproduct was then separated and recovered in filter containers, calcinedin the dry state at a temperature of 600 C. for minutes, and was thenground 1n a conventional Raymond mill.

The recovered composite TiOz pigment was soft and fiuffy, and extremelyfine in particle size. It represented a yield of the theoretical. Its pHvalue was 7.1 and, on analysis, it was found to contain 97.71% T102 (allrutile) and 1.6% A1203. Its tinting strength was 194.; its color 19:2Y;and its average particle size radius was .160 micron.

Although it is essential, in producing a pigment-quality T102 productunder the invention, that the temperatures, concentrations, andretention times used shall be controlled and correlated, the reactants,concentrations, volumes, ratios, temperatures, velocities, and timeswhich have been mentioned can be suitably varied. Thus, while titaniumtetrachloride and aluminum chloride comprise essential reactants in theprocess, other volatilizable metal halides, particularly chlorides whichyield white, insoluble oxides during the co-oxidation, such as thechlorides of .silicon, zirconium, antimony, zinc and tin, can

be employed in conjunction therewith, and in amounts to accord with theresults desired and the ultimate type of pigment product sought.

Such additional metal halides may be used individually with the titaniumtetrachloride and aluminum chloride or mixtures thereof can be employed,depending upon the type and use of the pigment being produced. Theamount of additional halide employed is usually relatively small, e. g.,ranging from 0.1% to 10% by weight, based on the weight of the titaniumtetrachloride and aluminum chloride.

Similarly, the amount of AlCls employed in the invention is relativelysmall or minor and need only range from, say, 0.1% to 10% by weight,based on the TiCh. When amounts under about and ranging from, say, about.5% to 4% are used, outstandingly beneficial effects have been found toresult, and hence such latter amounts are preferred for use in obtainingoptimum benefits hereunder.

The aluminum chloride may be mixed with the titanium tetrachlorideeither in liquid or vaporized state and then heated to a suitablereaction temperature prior to introducing the reactants into thereaction vessel. Alternatively, these reactants may be added separatelyto the reaction zone after their desired preheating.

As disclosed in the aforementioned Schaumann application, air, suitablyhumidified by H2O addition, comprises a preferred type ofoxygen-containing gas for use in the invention. However, other types aswell as amounts of oxidizing gases containing free oxygen (02) andsimilarly preferably moisture-enriched prior to use, can be employedherein, as can mixtures of such gases. Other useful types of gasesinclude oxygen, oxygen-enriched air, or mixtures of oxygen or air withvarious inert types (nitrogen, etc.) of gases.

Generally, it is preferred to operate the process with amounts ofoxidizing gas sufficient to provide about excess oxygen over thetheoretical so as to obtain a product gas containing about 30% C12 byvolume, when air is used as the source of oxygen, and 90-95% C12 whengaseous oxygen is employed, with but small or minor amounts of O2 andH01. The use of oxygen-enriched air will produce chlorine concentrationsintermediate be tween 30 and 90% C12 gas in the oxidation products.However, the invention is not limited to this, but can be operated usingeither excess or deficient concentrations of the oxidizing or titaniumtetrachloride reactant. In event of excess chloride use, the latter canbe separated from the oxidation products and reused in the system.

The amount of water vapor present in the oxidizing medium, whilepreferably ranging from .1-3%, may vary from, say, .05% to 5%, butshould not exceed 10%, these percentage amounts being based on the totalvolume of gaseous reactants being fed to the reaction zone. While therequired concentration of water vapor is preferably introduced into thereaction zone via and as a component part of the oxidizing agent, othermethods for insuring the presence of a sufficient quantity of H20 duringthe contemplated vapor phase oxidation reaction can be resorted to. Itbeing essential and critical to the invention that the water vapor bepresent in controlled quantity, any method insuring the presence of suchrequired quantity, or which will lower the amount present if too high,is contemplated as useful herein. Thus, the water vapor can becontinuously added, either directly and independently to the reactionzone itself, or as a component of the oxidizing medium being employedand introduced into such zone. Alternatively, it can be introduced witheither or both chloride reactants, or by first mixing part or all of thelatter reactants while in gaseous state and then suitably incorporatingthe desired quantity of water vapor into them prior to charging themixture into the reaction zone. Other methods for insuring-the presenceof the requisite amount of water vapor during the reaction, moreparticularly disclosed in said Schaumann application, can also beemployed, as can the process of forming the water vapor in situ of thereactants and through free hydrogen presence in the reaction Zonedisclosed in the co-pending application of H. H. Schaumann, Ser. No.713,382, filed November 30,1946 and issued as U. S. Patent 2,488,440dated November 15, 1949.

While reaction zone temperatures ranging from 900-1200" C. are preferredfor use, temperatures ranging from 800 C. to 1350 C. are alsoemployable. These temperatures can be readily obtained in a large-scale,commercial type of operation, by either separately preheating each orall reactants to a temperature adequate to insure on their admixture andreaction temperatures of the order indicated. They can be maintainedeither by means of the heat generated from the oxidation reaction or byexternally heating the reaction zone or vessel,

sel and into the reacting gases.

be produced in this invention.

The reactants used can be separately preheated by subjecting each to anequivalent heating temperature, or, if desired, the oxodizing gas may bepreheated to a temperature above or below that to which the titaniumtetrachloride and other metal halide is subjected, whichever ispreferred. Any conventional type equipment can be used in the preheatingoperation, including any suitable type of electrical resistanceapparatus or devices which will pass the reactants in direct or indirectheat exchange relationship with a heat-imparting medium. A useful typefor the purpose comprises one in which the reactants pass over heattransfer surfaces heated directly by combustion of fuels or indirectlyby circulation of a suitable heat transfer medium.

Normally, the oxidation reaction is effected under atmosphericpressures, but, if desired, it may be conducted under superorsubatmospheric pressures. Similarly, any type or size of reaction vesselconforming to the scale of operation intended can be used, withequipment of such design and dimension as will permit a continuous flowof reactants through the reaction vessel, especially the oxidationchamber, being preferred for use to insure a continuous, asdistinguished from a discontinuous or batch, type of operation beingeffected. While a continuous process is preferred, a batch orsemicontinuous operation can also be resorted to.

The time of retention of the reactants within the reaction zone is alsoquite important and critical in the production of pigment-quality TiOz.Generally, the retention time of all reactants within the mixing andreaction zone must not exceed about 5 seconds nor be less than about .01of a second, with a preferred time, to insure recovery of an optimumquality pigment, ranging from .1 to 1 second.

As contemplated in said Schaumann application, both anatase and rutileT102 pigments can In producing rutile of optimum pigment qualities, theoxidation reaction should be effected under such a combination ofconditions that there will exist:

(a) A minimum moisture concentration in the reacting gases;-

(b) A minimum preheating temperature for the reactants will be used anda thorough, rapid admixture of such reactants will be effected;

(c) A minimum retention time of reactants and products in the oxidationchamber will prevail, sufiicient only to effect substantially completeconversion of the TiCll to T102 and growth of the T102 pigment particlesto the desired size; and

(d) A quick cooling or quenching of the products from the oxidationreaction after formation of the desired T102 particle size will be hadso as to prevent overgrowth of the pigment particles.

These variables are interdependent and optimum values, within the limitsspecified for moisture content in the reacting gases, preheating andreaction zone temperatures and retention time in the oxidation chambermust be predetermined for a particular apparatus to obtain therefrom thedesired particle size rutile pigment. The preferred relationship betweenthese critical variables is dependent upon such factors as manner andspeed of mixing of the reactants, size and shape of the oxidationchamber, etc., as well as upon the particle size desired in the pigmentT102.

The preheating temperature to which the reactants are subjected has animportant bearing upon the ultimate type, crystallinity, and characterof the T102 pigment. In anatase production, it is usually desirable thatlower preheating temperatures with resulting lower reaction chambertemperatures be resorted to than is necessary in the production ofrutile. The preferred, most useful temperature used will depend uponsuch factors as the scale of the involved operation, the size and shapeof the reaction chamber, and the rapidity with which gas mixing can beefiected. In producing rutile, preheating temperatures adequate toinsurea mixed gas temperature of at least 350 0., and preferably above 400 C.,are usually required. In anatase production, preheating temperaturessufiicient to afford a mixed gas temperature ranging from below 350 C.to not lower than 100 C. are usually adequate. While a preheatingtemperature of at least 350 C. is suggested for rutile production, itwill be found that as the size of a given operation increases, theamount or degree of preheating temperature required will decreasesomewhat. Hence, temperatures below said 350 C. and to as low as 250 C.may be employed in some instances. When preheating temperatures below400 C. are employed, the pigment product may contain appreciablequantities of combined chlorine (oxychlorides). These are readilydecomposed upon subjection of the product to the mild calcinationtreatment herein contemplated.

The titanium tetrachloride and aluminum chloride reactants usedpreferably comprise high-purity materials free of contaminatingimpurities, such as those of vanadium, iron, copper, etc and which willthus insure production of a product exhibiting exceptionally highpigment whiteness and brightness characteristics. The TiCh can beobtained, for instance, by chlorinating a titaniferous are, such asilmenite, and purifying the product through careful fractionaldistillation. Examples of other useful presently clearly understood. Itappears, however, that four involved reactions of varying degree ofexothermicity must be considered Titanium tetrachloride reacts avidlywith Water vapor, and it appears that under the controlled conditionswhich prevail when the reactants are mixed (high concentration TiCh andlow concen- K'cal tration of H20) that reaction (1) first formsextremely minute T102 crystallites, well dispersed throughout thegaseous mixture. Control over the size, crystalline form, and number ofthese nucleating particles is effected by the amount of water presentand the temperature conditions under which they are permitted to form.Under the'prevailing, controlled reaction conditions,'a continuous,fresh supply of nucleating particles is provided onto which T102 fromreaction (2) can precipitate to build up or grow into Ti02 particles ofdesired pigment dimensions. Since the A1C13 is present in only minoramounts, and is competing with TiCl4 in relatively high concentrationfor reaction with H20 vapor, it is unlikely that significant amounts ofalumina are formed by reaction (3), in spite of its higher heat ofreaction. The major portion of the A1203 is apparently formed byreaction of A1C13 with oxygen, since concentrations, temperature, andthermal energy conditions are more'favorable for reaction Therefore,reaction (4) then proceeds simultaneously with reaction (4) than forreaction (3).

(2) and alumina is deposited continuously with T102 on the nucleatingparticles formed by re' action (1). However, TiOz and A1203 aredissimilar in crystal structure and the A1203 cannot fit directly intothe crystal lattice of TiOz. The simultaneous precipitation from the gasphase of large amounts of T102 compared with the quantity of A1203formed, together with the extremely rapid formation of A1203, suppressestrue crystallinity in the A1203. It is believed that under theprescribed conditions, the minor amount of alumina is deposited inamorphous form through out and on the surface of the TiO2 particles.

Quite surprisingly, the benefits imparted to the pigment T102 whenalumina is introduced in this manner cannot be achieved by separatelyreacting aluminum chloride in the vapor phase with oxygen or Watervapor, or mixtures of the two, and then intimately mixing the A1203 withTi02 which has been separately prepared. The ad vantages of theinvention are realized only when the simultaneous reactions betweenTiCll, A1013, oxygen and water. vapor under the indicated con- 11ditions of concentration, temperature and reaction zone retention timesare effected.

We claim as our invention:

1. A process for obtaining pigmentary titanium dioxide which comprisesreacting in the vapor phase, and at temperatures ranging from 800- 1350-C., titanium tetrachloride and a small amount of aluminum chloride withan oxygencontaining gas, eflecting said reaction over a time periodranging from .01 to seconds and in the presence of from .05 to byvolume, based on the total volume of gases being reacted, of watervapor, and thereafter recovering the T102 product from the resultingreaction products.

2; A process for producing pigmentary titanium dioxide which comprisesreacting in the vapor phase and at a temperature of at least 800 C.titanium tetrachloride together with from 0.1% to 10%, by weight, basedon said tetrachloride, of aluminum chloride with an oxygen-containinggas, effecting said reaction over a time period ranging from .01 to 5seconds and in the presence of from .05% to 10% by volume, based on thetotal number of gases being reacted, of water vapor, and thereafterrecovering the T102 product from the resulting reaction products.

' 3. A process for producing pigmentary titanium dioxide which comprisesreacting titanium tetrachloride, together with from 0.1% t 10%, byweight, based on said tetrachloride, of aluminum chloride, with anoxygen-containing gas, effecting said reaction over a time periodranging from .01 to 5 seconds in the vapor phase at temperatures rangingfrom 8001350 C., and in the presence of regulated quantities of watervapor ranging from .05% to 10% by volume, based on the total volume ofgases being reacted, and then recovering the T102 pigment from theresulting reaction products.

4. A process for producing pigment-quality titanium dioxide, comprisingreacting in the vapor phase titanium tetrachloride, together with from.1 to 10% of aluminum chloride, calculated as the oxide, with anoxygen-containing gas, at temperatures ranging from 900-1200 C. and inthe presence of from 05% to 10% by volume of water vapor, based on thetotal volume of gases being reacted, efiecting said reaction over areaction zone retention time period ranging from .01 to 5 seconds, andthen subjecting the, resulting T102 product to a mild calcinationtreatment.

5. A process for producing pigment-quality rutile which comprisesreacting in the. vapor phase and at temperatures ranging from 900- 1200C., titanium tetrachloride and an amount of aluminum chloride equivalentto from .1% to 10% calculated as the. oxide, with an oxygencontaininggas, eifecting said reaction over a time period of from .01 to not toexceed 5 seconds and in the presence of an amount of water vapor rangingfrom .1% to 5% by volume, based on the total volume of gases beingreacted, calcining the recovered TiOz product at a temperature rangingfrom 500800 C., and subjecting the calcined product to mechanicalmilling treatment.

6. A process for producing a rutile T102 prodnot having a substantiallyneutral pH value, which comprises reacting, in the vapor phase and attemperatures ranging from 900-1200 0., a mixture of preheated titaniumtetrachloride and an amount of aluminum chloride equivalent to from .3%to 3% A1203. based on the amount of titanium pigment being produced,with air containing an amount of water vapor ranging. from;

12 .1 to 5% by volume, based on the total volume of gases being reacted,effecting said reaction over a time period ranging from .01 to not toexceed 5 seconds, and then calcining the recovered TiOz product at atemperature of from 500- 700 C.

7. A process for producing pigment-quality rutile exhibiting improvedbaking discoloration and yellowing resistance properties in coatingcompositions, comprising reacting in the vapor phase, and attemperatures ranging from 900- 1200" 6., titanium tetrachloride admixedwith an amount of aluminum chloride equivalent to from .1% to 10%,calculated as the oxide, with air containing from .1% to 5% of watervapor by volume, based on the total volume of gaseous reactants, priorto said reaction separately preheating the chloride mixture and air to atemperature of at least 350 C., efiecting said reaction over a timeperiod ranging from .01 to 5 seconds, quickly quenching the resultingreaction products to a temperature below 600 6., there-- after calciningthe cooled product in the dry state at temperatures ranging from 500-7000., and then mechanically milling and recovering the finished product.

8. A process for producing pigmentary T102 which comprises reacting inthe vapor phase and at temperatures ranging from about 900 to 1200 C.,titanium tetrachloride and an amount of aluminum chloride equivalent tofrom .3% to 3%, calculated as the oxide, with an oxygen-containing gas,effecting said reaction in the presence of an amount of water vaporranging from .1% to 5% by volume, based on the total volume of gasesbeing reacted, and in a reaction'zone in which the reactants remain fora time period of from .1 to 1 second, recovering the resulting T102pigment from the reaction products, and subjecting it to calcination ata temperature ranging from 500 to 700 C.

9. A process for producing pigmentary TiOz which comprises reacting inthe vapor phase and at temperatures ranging from 900 to 1200" 0.,titanium tetrachloride and an amount of aluminum chloride equivalent tofrom .3% to 3%, calculated as the oxide, with an oxygen containing gas,efiecting said reaction in the presence of an amount of water vaporranging from .1% to 5% by volume, based on the total volume of gasesbeing reacted, and in a reaction zone in which the reactants remain fora time period ranging from .1 to 1 second, quickly removing the reactionproducts from said reaction zone and thereupon cooling them to below 600C. within from 1 to not to exceed 10 seconds, and then subjecting therecovered TiOz product to calcination at temperatures ranging from 500to 700 C.

IGNACE JOSEPH KRCHMA. HOLGER HEINRICH SCHAU'IVIANN.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,967,235 Ferkel July 24, 19342,347,496 Muskat et a1 Apr. 25, 1944 2,394,633 Pechukaset a1 Nov. 24,1946 FOREIGN PATENTS Number Country Date 541,343 Great Britain Nov. 24,1941'

1. A PROCESS FOR OBTAINING PIGMENTARY TITANIUM DIOXIDE WHICH COMPRISESREACTING IN THE VAPOR PHASE, AND AT TEMPERATURES RANGING FROM 8001350*C., TITANIUM TETRACHLORIDE AND A SMALL AMOUNT OF ALUMINUM CHLORIDE WITHAN OXYGEN CONTAINING GAS, EFFECTING SAID REACTION OVER A TIME PERIODRANGING FROM .01 TO 5 SECONDS AND IN THE PRESENCE OF FROM .05 TO 10% BYVOLUME, BASED ON THE TOTAL VOLUME OF GASES BEING REACTED, OF WATERVAPOR, AND THEREAFTER RECOVERING THE TIO2 PRODUCT FROM THE RESULTINGREACTION PRODUCTS.